A typical prior art flow control valve includes a block formed with a cylindrical bore containing a piston or spool having several enlarged diameter portions or lands engaging the cylindrical bore and connected by smaller diameter portions. The block is formed with a number of passageways or ports in communication with the interior of the bore at various places along its length and adapted to be connected exteriorly of the valve to (1) a supply of fluid under pressure, (2) a fluid return line or reservoir, and (3) first and second conduits leading to opposite sides of a load device such as a hydraulic ram. When the spool is in its neutral position, the lands occlude some or all of the ports in such a way that no fluid flows through the valve. In operation, the spool is displaced axially to one side or the other of its neutral position by an external force, for example, by a pilot valve. When so displaced, the lands partially or fully expose certain ports in such a fashion that the fluid under pressure flows into one of the load conduits while fluid from the other load conduit flows through the valve to the return line. As the spool is first displaced a short distance from its neutral position, fluid flows from a relatively high pressure area through the small orifice adjacent to the rim of the land to a relatively low pressure region having the relatively large volume of either the cylindrical bore adjacent to a reduced diameter portion of the spool or to one of the ports in the block, depending upon the direction of flow. In either case, the flow through the small orifice into the large volume at low pressure results in high velocity and high turbulence. These conditions in turn cause a high noise level and rapid erosion of the edge of the land.
It is a general object of the present invention to provide an improved fluid-flow control valve.
Another object of the invention is to provide a fluid-flow control valve which is very quiet in operation.
Another object of the invention is to provide a fluid-flow control valve having a very long life.
A more specific object of the invention is to provide a fluid-flow control valve in which the flow of fluid is controlled without generating high fluid velocities with the result that the valve operates very quietly and exhibits an especially low rate of erosion of the lands.